ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 409 



numerous here. During the course of the next week, how- 

 ever, Nitzschia closterium rapidly increased in quantity, 

 until not only the sides of the jar were coated with it, but the 

 whole mass of the water became thick and opaque. By this 

 time the plankton diatoms had all disappeared, with the 

 exception of those which may survive for a considerable 

 period amongst the precipitate at the bottom of the jar. 

 Bottom diatoms (Navicula, etc.) had begun to grow on the 

 sides of the jar, and small green and brown algre (Pleuro- 

 coccns mucosus, Ectocarpus, etc.) also appeared. 

 Infusoria (Euplotes and other smaller forms) then became 

 numerous, and as the Nitzschia and bottom diatoms in- 

 creased on the glass, large numbers of Amoeba? made their 

 appearance among them. The jars continued in this con- 

 dition for many months, the algte becoming more and more 

 predominant. 



From these experiments, as well as from instances of mixed 

 cultures obtained in the course of our attempts to secure 

 persistent cultures of single species of diatoms, it seems usual 

 that, in a culture obtained by inoculating Miquel sea-water 

 with plankton taken freshly from the sea^ the true plankton 

 diatoms are the first to develop in considerable numbers. 

 Subsequently bottom diatoms and algae of various kinds 

 become abundant, and the true plankton forms die out. 



A complete explanation of this sequence of events would 

 probably be of a very complicated character, and we have 

 practically no evidence from our experiments which bears 

 veiy directly on the question. It would seem, however, that 

 the early predominance of the plankton forms in the cultures 

 would naturally follow from the fact that, in the plankton 

 material used for inoculation, these plankton forms are 

 numerous, whilst bottom diatoms and spores of algse are rare. 

 The subsequent very great predominance of such a species as 

 Nitzschia closterium may be due simply to a very much 

 more rapid growth rate, though it is difficult to avoid the 

 impression that the organisms, which finally take possession 

 of the cultures, are in some way directly inimical to those 



